Driver unit for loudspeakers



Oct. 28, 1958 s. E. LEVY 2,858,377

DRIVER UNIT FOR LOUDSPEAKERS ATTORNEY Oct. 28, 1958 s. E. LEVY 2,858,377

DRIVER UNIT FOR LoUDsPEAxERs Filed April 29, 1953 2 Sheets-Skaail 2United rates DRIVER UNrr Fou LOUDSPEAKERS Sidney E. Levy, White Plains,N. Y., assiguor of one-haii to Arthur Blumenfeld, New York, N. Y.

Application April 29, 1953, Serial No. 351,962

19 Claims. (Cl. 179-1155) The present invention relates to loudspeakerdriver units, and more particularly to a novel driver unit of .both adirect and indirect radiator type having acoustically isolated dualconcentric or coaxial throats.

Heretofore, loudspeaker driver units usually have been so constructed asto utilize the acoustic energy generated from only one surface of thediaphragm by directing this energy to a throat or central orifice forentrance into a suitable horn or trumpet, while the sound energygenerated by or radiated from the reverse side of the diaphragm isconfined to and trapped in a relatively air-tight chamber, or is trappedwithin the housing or shell f the driver unit and is not directed intothe atmosphere, or is otherwise dissipated as wasted energy.,

Other known driver units have been so constructed as :to utilize thesound generated by the rear vsurface of the diaphragm, in addition tothat generated by the front surface thereof, by directing the rear soundgeneration to a vseparate horn or trumpet which is on a common axis withthe front horn or trumpet. 4In this type of construcztion the respectivesound generations travel in directions '180 apart.

vIt is an object of the present invention to provide a novel loudspeakerdriver unit which is so constructed as to collect the acoustic energygenerated by the rear sur- Aface of the diaphragm and direct the sameforwardly so that it is directed in the same direction and on the sameaxis as sound generated by the front surface of the diaphragm.

'A further object is to provide a novel loudspeaker driver unit whichcollects the sound generated by the rear surface of the diaphragm andacoustically isolates the rear sound generations and directs the sametowards a central neck or throat which is coaxial with the direction oftravel of sound generated by the front of the diaphragm, this neck beingadapted to be connected to a horn through which the two acoustic wavesare projected coaxially into the atmosphere.

Specifically, it is an object of this invention to provide a loudspeakerdriver unit which includes an outer shell, a magnetic pot assemblysuitably mounted in said shell and spaced therefrom, a centralpole-piece carried by said pot assembly, said pole-piece having anaxially extended opening therethrough communicating with the spacebetween the shell and the pot assembly, a diaphragm mounted in the spacebetween the shell and the magnet assembly, a barrier defining anisolated air chamber in front of the diaphragm and with the shelldefining a second isolated air chamber concentric with the first airchamber and communicating with the. opening through the pole-piecethrough the space between the magnetic pot assembly and the shell,whereby sound generated by the front of said diaphragm is directedaxially through the first-mentioned chamber, and sound generated by theback of the diaphragm will be directed through the polepiece and thespace between the pot assembly and the v'shell and through thesecondmentioned air chamber` Another specific objective of the presentinvention is ice to provide a loudspeaker driver unit which includes anouter shell, a magnetic pot assembly suitably mounted in said shell andspaced therefrom, said pot assembly including a central pole-piecehaving a plurality of openings therethrough, a vibratable diaphragminterposed between said pot assembly and the rear wall of said outershell, and a barrier carried by said magnetic pot assembly at theforward side thereof, said barrier defining a central throattherethrough in communication with theA openings through the pole-piecefor conducting sound generated by the forward surface of the diaphragmto a horn, and said barrier defining with the shell a second throatconcentric with the first-.mentioned throat and communicating throughthe space around said pot assembly with the space at the rear side ofsaid diaphragm for conducting sound therefrom to said horn.

Other objects, advantages or features of construction will behereinafter described or will become apparent t0 those skilled in theart, and the novel features of the present invention will be defined inthe appended claims.

In the drawing:

Fig. 1 is a longitudinal sectional view taken on the central plane of adriver unit embodying the present iuvention, said driver unit beingadapted to be connected to a horn or other sound directing unit such asthat shown in broken lines; i

Fig. 2 is -a view in front elevation of the driver unit alone, with aportion thereof broken away;

Fig. 3 is a longitudinal sectional view taken on the central plane ofanother form of driver unit embodying the present invention, this driverunit also being adapted to be connected to a horn or othersound-directing unit such as that shown in broken lines in Fig. l; and

Fig. 4 is a view in front elevation of the driver unit of- Fig. 3.

Like reference characters designate corresponding parts in the figuresof the drawings and in the following detailed description.

One form of driver unit embodying this invention, as shown in Figs. land 2 includes an outer housing or shell 1, an inner magnet or potassembly 2, a diaphragm '3, a partition or baflie 4, and perforatedspacer elements 5 and 5'.

The housing 1 is preferably made in two partsand has` a rear, cup-likeshell portion 6 disposed in abutting engagement with a forwardlyprojecting closure 7 having same in abutting engagement, with acompressible annular gasket or washer 4' therebetween.

Suitably mounted in and carried by the housing or shell l is the magnetor pot assembly 2 which includes an annular plate 9 of magnetic materialhaving a central opening 9' therein. provided with a plurality ofcircumferentially spaced L- shaped ribs 6 which serve to center the potassembly and maintain the same in spaced relation to the inner rear faceand the annular wall of the shell 6. Engaged with the annular member 9is an annular or ring magnet element 10 which is operatively connectedto another annular plate il at the rear side of the member 10, thisplate ll having a central opening i2 therethrough. Operatively connectedto the plate 11 about the margin of the opening 12 is a centralpole-piece13, this polepiece 13 having a rearwardly diverging centralopening 14 therethrough. A centering washer 15 of annular form issuitably secured to the plate 9 and projects radially inward intocontact with the outer margin of the pole- Patentecl Oct. 28, 1958 Theshell 6 at its inner rear side is piece 13, this centering washer beingof a non-magnetic material.

The diameter of the pole-piece 13 is less than the diameter of theopening 9 through the annular plate 9, thus providing an air gap 16therebetween, and a cylindrical voice coil 17 which is suitably securedto the diaphragm 3 in any conventional manner projects into the air gap16.

The diaphragm 3 preferably has a domed central portion 18 interconnectedby compliant ribs 19 with a marginal fiange 20, this marginal ange 20being secured between the pair of annular spacer washers or gaskets 5,which are interposed between the forward face of the annular plate 9 andthe opposing inside surface of the closure portion 7, with the flange ofthe diaphragm 3 clamped between the washers 5, 5. Y

The bathe or separator 4 is also provided with a niarginal ange 21 whichis clamped between the washers 5, 5', this bafiie 4 tapering forwardlyand inwardly towards the axis of the driver unit and extending forwardlythereof to form a central throat 21. About the throat portion 21 of theseparator 4, the neck 8 of the housing 1 is provided with a centeringcollar or spider 22 having annularly spaced radial connecting ribs 23spaced there around. As best seen in Fig. 2, the spaces intermediate theribs 23 define arcuate passageways 24.

The washers 5, 5 are respectively provided with a suitable number ofradial openings 25, 25 therethrough, these openings as shown in thedrawing being in the form of round passageways, and the voice coil 17 islikewise provided with a suitable number of annularly spaced openings 26therethrough, the latter openings shown in the drawing also being in theform of round apertures.

As is best seen in Fig. 1, the baffle or separator 4 divides the housing1 into two acoustically isolated chambers 27 and 28. The chamber 27 isdefined between the forward or outer surface of the separator 4 and theinner surface of the closure 7, and the openings 2S through the forwardwasher 5 establish communication between the chamber 27 and the zone ofthe housing 1 in which the pot assembly 2 is mounted. The openings 25through the rearward washer 5 serve to establish communication betweenthe space behind the diaphragm 3 and the space between the pot assembly2 and the housing, and the openings 26 through the voice coil 17establish communication between the space within the confines of thevoice coil and the space between the compliant section 19 of thediaphragm and the plate 9 of the pot assembly. Communication betweenthese latter spaces is also established through the air gap 16 aroundthe inner or free end of the voice coil 17. The air chamber 28 isdefined between the inner or rearward faces of the separator 4 and theforward face of the diaphragm 3, respectively.

The shape or contour of the isolating partition 4 and thecontour of theinner surface of the closure portion 7 of the housing are designed toprovide a cross-sectional area for each of the chambers 27 and 2S whichwill maintain a maximum acoustic efhciency, since abrupt changes inthese areas would result in an undesirable restriction or pocket, withattendant deleterious effects upon the frequency response andsensitivity of the loudspeaker driver.

Sound generated by the forward surface of the diaphragm is confined tothe chamber 28 and thus is preferably directed to the throat 21 of theseparator 4 without any bend or circuitous pass, and thus this directand relatively short path is primarily for the high frequency soundsgenerated by the diaphragm. On the other hand. however, the soundsgenerated by the rear surface of the diaphragm 3 will be caused totraverse a number of bends in its path to the chamber 27, with resultantloss of high frequency energy because of path length differences at thebends which tend to trap or cancel the higher frequencies. Therefore therefiex energy from the rear 4 surface of the diaphragm becomes usefulfor the middle or low frequency bands of sound waves.

Since the forward portion of the neck 8 defines an annular throat 27concentrically disposed about the throat 21 of the separator 4, thedriver unit produces two acoustic waves, namely, a high frequency waveand a low frequency wave, both emerging from a common outlet. When sucha driver unit is associated with a horn such as that shown in brokenlines in Fig. 1, sound may be reproduced by a single voice coil anddiaphragm and uliimateiy directed into the atmosphere in two separatewaves, with both Waves transmitted in the same direction on a commonaxis.

The horn shown in broken lines in Fig. 1 is the subject matter of mycompanion application tiled concurrently herewith, and therefore willonly be described generai'iy in the present application.

The horn assembly comprises a supporting member or head 31 adapted tothreadedly engage the threaded neck S of the housing 1 of the driverunit. This supporting member 31 is provided about its outer margin witha dared bell 32, the forward surface of the member 31 being arcuatelyformed at 31 so as to merge with the curvature of the bell 32. At itscenter, the member 31 is provided with a spider-like support 33 havingarcuate openings 34 therethrough which correspond substantially to theopenings 24 in the spider 22. Suitably coaxially mounted on the member31 are an intermediate annular wall or partition 35 and an inner annularwall or partition 36, The inner wall 36 is of such a diameter as tosubstantially match the throat 21 of the separator 4 and ares ordiverges gradually towards its forward end so as to provide a relativelyshort high frequency horn which preferably terminates at its extremeforward end in a widely flared bell 36. The space between the inner wall36 and the intermediate wall 35` communicates with the chamber-27 andthus constitutes a sound path for low and middle frequency sound wavesgenerated by the rear of the diaphragm 3, and this latter sound path isreflexed at the forward end of the wall 35 3S to the supporting member31 of the horn assembly.

The arcuate surface 31 of the supporting member 31 reexes the lowfrequency sound path a second time from whence the low frequency soundpath again extends forwardly.

The path of sound waves generated by the forward side of the diaphragm 3is indicated by solid arrows, and

it will be noted that this path is relatively short and straight. Thepaths followed by the sound waves.l generated by the rear side of thediaphragm 3 are indicated by broken arrows, and it will be seen that thelatter sound paths are circuitous or tortuous.

Tracing out the paths followed by the soundwaves generated by the rearface of the diaphragm, it is seen from the broken arrows in Fig. 1 thatsound generated by the central portion of the diaphragm 3 passesrearwardly through the opening 14 in the pole-piece 13 and is thencaused to spread by a conical projection l" on the inner face of thehousing 1, into the space 40 between the pot assembly 2 and thehousing 1. This space 4@ extends completely around the outer peripheryof the pot assembly 2, and the sound waves thus are directed to theopenings 25 through the forward washer 5 through which the sound wavespass in a radially inward direction into the chamber 27. From thechamber 27, the sound waves pass through the spider openings 24 and 34of the assembly and into the reflexed sound passage of the horn.

In addition, some of the sound waves generated by the rear arca of thediaphragm lying close to the voice coil may follow either or both of twopaths, Sound waves following one of these paths pass rearwardly throughthe air gap 16 between the inner face of the voice coil and the outerperiphery of the pole-piece and are then reflexed by the centeringwasher and travel forwardly through the air gap 16 between the outerperiphery of the voice coil and the inner margin of the plate 9, wherethey join with sounds following the other of the two paths which isradially through the openings 26 in the voice coil 17. From here, thesound waves travel radially outwardly through the space 41 between thediaphragm and the plate 9 and then through the openings in the rearwasher 5 to the space 40, where they join the sound waves following thepath through the central pole-piece and continue along the same pathabove described through the openings 25 in the washer 5 and so on intothe horn.

Inherently, the sounds ultimately reaching the atmosphere from theforward face of the diaphragm 3 will be those of the high frequencyrange, whereas the sounds generated by the rear face of the diaphragm,by reason of their circuitous paths, will be those of the intermidiateor low frequency range, but these sounds of the different frequencyranges will nevertheless be projected in the same direction on the sameaxis and on a similar wave front.

Referring to Figs. 3 and 4, there is shown another form of the presentinvention.

In this form of the invention, the housing or shell 101 includes a pairof complemental housing parts 102, 103, each preferably having aplurality of radially projecting ears 104 and 105 through which athreaded fastener 106 extends. An annular, compressible washer 107 isdisposed between the opposed faces of the housing parts 102 and 103 toseal the housing against sound losses and to facilitate assembly of thedriver unit.

Mounted within the housing 101 and spaced therefrom is a magnetic potassembly including a rear annular plate 108 of magnetic material havinga central opening 109 therethrough, an annular magnet member 110 and aforward annular plate 111 of magnetic material having a central opening112 therethrough. A central pole-piece 113 is disposed in the opening109 in plate 108 and engages at its forward end with the plate 111. Atthe forward side of the plate 111 is an axially extended barrier member114 having a radial ange 115 thereon seating on the plate 111 and havingan axially extended annular flange 116 seating in the housing 112through the plate 111. Extending axially through the barrier 114 is asound passage 117.

At the other side of the pot assembly and engaged with the rear side ofthe plate 108 is a vibratable diaphragm 118 having a voice coil 119carried by its central portion, this voice coil projecting into theair-gap 120 defined between the pole-piece 113 and the inner peripheryof the plate 108.

The magnetic pot assembly, together with the barrier 114 and thediaphragm 118, are located and maintained in spaced relation to theinside surface of the housing 101 by means of a plurality ofcircumferentially spaced L-shaped ribs 122 and 123 at the inside cornersof the respective housing parts' 102 and 103. The ribs 122 engage aresilient washer 124 interposed between a marginal flange 125 of thediaphragm 118 and the ribs 122, and the ribs 123 engage the forwardsurface of the flange 115 of the barrier 114, whereby when the housingparts are secured together by the screws 106, the pot assembly, thebarrier and the diaphragm are clamped together between the ribs 122 and123. The ribs 122 and 123 also engage the outer periphery of the potassembly and hold the `pot assembly in coaxial spaced relation to thehousing.

The forward end of the housing part 103 is provided with a reducedthreaded neck 126, the inner periphery of which is spaced from the outerperiphery of the barrier 114 so as to provide a sound passage 127communicating through the space 128 between the pot assembly and thehousing with space 129 between the rear side of the diaphragm 118 andthe housing. The central pole-piece 113 is preferably provided with aplurality of openings 130 therethrough, which openings establishcommunication between the sound passage 117 through the barrier 114 andspace 131 between the diaphragm and the polepiece. Thus, soundsgenerated from opposite sides of the diaphragm 118 are free to travelthrough acoustically isolated sound paths to dual concentric throats 117and 127, from whence these separate sound waves may pass into a suitablehorn such as that shown in broken lines in Fig. l, which horn is adaptedto be connected to the threaded neck 126 of this form of the driverunit.

In use, sound waves generated by the rear face of the diaphragm 118 willtravel from space 129 around the outside of the pot assembly, throughspace 128, and out through the throat 127. This sound path is designatedby the broken directional arrows, and since this sound path is long andtortuous, it is primarily suited for the conduction of relatively lowfrequency sound waves.

On the other hand, sound waves generated from the inner or forward sideof the diaphragm 118 will pass through the openings 130 through thecentral pole-piece and through the throat 117, as indicated by the solidarrows, and because of the fact that this' path is relatively short andstraight, it is primarily suited for the conduction of relatively highfrequency sound waves.

Thus, the driver unit of each of the two illustrative forms of thepresent invention will direct the sound waves generated from oppositesides of a single diaphragm through acoustically isolated sound paths todual concentric throats from which these respective sound waves areemitted on the same axis, in the same direction, and on a similar wavefront. It is to be understood that in referring to a central pole-piecehaving an opening therethrough, as described in the specification withrespect to the elements designated `13 and 113, and as defined in theclaims, any appropriate form of magnet having an opening through aportion thereof disposed over the diaphragm may be employed.

While the specific details have been herein shown and described, theinvention is' not confined thereto as changes and alterations may bemade without departing from the spirit thereof as defined in theappended claims.

I claim:

1. A loudspeaker driver unit comprising an outer shell, a magnetassembly mounted in said shell in spaced relation thereto, said magnetassembly including a central polepiece having a central sound passagetherethrough communicating with the space between said shell and saidmagnet assembly, a diaphragm mounted in said shell, means engaged aboutthe margin of said diaphragm and projecting axially to form a soundpassageway therethrough on one side of said diaphragm, said meanstogether with said shell defining a second sound passageway concentricwith the first passageway and acoustically isolated therefrom, and meansestablishing communication between the second sound passageway and thespace between the magnet assembly and the shell.

2. A loudspeaker driver unit comprising a shell, a magnetic pot assemblymounted in said shell, a central pole-piece in said pot assembly anddefining an air-gap between the pole-piece and a portion of said potassembly, a vibratable diaphragm spaced from said pot assembly and fromsaid shell and having a voice coil extending into said air-gap,separator means engaged about the margin of said diaphragm andprojecting axially therefrom and forming a hollow sound passage forsound generated from one side of the diaphragm, said shell surroundingsaid separator means in spaced relation thereto and defining a secondsound passage acoustically isolated from the first sound passage andconcentric therewith for conducting sound generated from the other sideof said diaphragm, and means establishing communication between saidsecond sound passage and the space between the diaphragm and the potassembly.

3. A loudspeaker driver unit as defined in claim 2, wherein thelast-mentioned means comprises a pair of washers having radial openingstherethrough, said washers engaging said diaphragm about the marginthereof, with one of said washers disposed on one side of said diaphragmand the other of said Washers disposed on the other side of saiddiaphragm.

4. A loudspeaker driver unit as defined in claim 2, wherein thelast-mentioned means comprises a pair of washers having radial openingstherethrough, said washers engaging said diaphragm about the marginthereof, with one of said washers disposed on one side of said diaphragmand the other of said washers disposed on the other side of saiddiaphragm, and said separator means including a marginal flange securedbetween said washers with the margin of the diaphragm.

5. A loudspeaker driver unit as defined in claim 2, wherein thelast-mentioned means comprises a central opening provided in saidpole-piece, and said pot assembly is spaced from said shell to providean annular space communicating with the opening through said pole-pieceand the second sound passage aforesaid.

6. A loudspeaker driver unit as defined in claim 2, wherein thelast-mentioned means comprises a central opening provided in saidpole-piece, and said pot assembly is spaced from said shell to providean annular space communicating with the opening through said pole-pieceand the second sound passage aforesaid, and said shell having a conicalprojection extending into the opening through the pole-piece.

7. A loudspeaker driver unit as defined in claim 2, wherein the voicecoil is provided with a plurality of openings therethrough.

8. A loudspeaker driver unit as defined in claim 2, wherein a centeringwasher bridges the air gap in spaced relation t the voice coil and formsa sound passage around the end of said voice coil.

9. A loudspeaker driver unit as defined in claim 2, wherein thelast-mentioned means includes a washer supporting the diaphragm inspaced relation to the pot assembly and having a plurality of passagesextending through said washer.

l0. A loudspeaker driver unit comprising an outer shell, a magnetic potassembly mounted in said shell in spaced relation thereto and definingwith said shell a sound passage therebetween, a central pole-piece insaid pot assembly, said pole-piece having a central openingtherethrough, a vibratable diaphragm disposed between said pot assemblyand a portion of said shell and overlying said pole-piece in spacedrelation thereto, said pole-piece being spaced from a portion of saidpot assembly and forming an air gap therebetween, said diaphragm havinga perforated voice coil having a free end extending into said air gap,means closing one end of said air gap and forming a sound passage aroundthe free end of said voice coil, a perforated washer interposed betweenthe marginal edge of the diaphragm and said pot assembly, anotherperforated washer interposed between the marginal edge of said diaphragmand the shell, an annular separator having a marginal flange disposedbetween the diaphragm and the second-mentioned washer, said separatorbeing in spaced relation to said shell and extending axially to form athroat for sound generated by the adjacent side of said diaphragm, andsaid shell surrounding the throat of said separator and forming a secondthroat concentric with the first throat.

ll. A loudspeaker driver unit comprising an outer shell, a magnetic potassembly mounted in said shell in spaced relation thereto and definingwith said shell a sound passage therebetween, a central pole-piece insaid pot assembly, said pole-piece having a central opening therethroughcommunicating at one end with the sound passage aforesaid, a diaphragmdisposed between said pot assembly and a portion of said shell andoverlying said pole-piece in spaced relation thereto, said pole-piecebeing in spaced relation to a portion of said pot assembly and definingan air gap therebetween, said diaphragm having a voice coil extendinginto said air gap, spacer means having sound passages therethrough andinterposed between said diaphragm and said shell, and separator meansdisposed between said diaphragm and said shell and forming therewith apair of acoustically isolated concentric sound passages, one of saidconcentric sound passages communicating through the passages in saidspacer means with the sound passage between the pot assembly and theshell, and the other of said concentric sound passages being confinedbetween said diaphragm and said separator means.

12. A loudspeaker driver unit comprising a shell, a diaphragm in saidshell, means also in said shell for vibrating said diaphragm, aseparator dividing said shell into two acoustically isolated soundpassages leading respectively to opposite sides of said diaphragm, saidshell having a reduced neck forming a throat for one of said soundpassages, and said separator having a reduced neck concentric with andspaced from said neck of the shell and forming a throat for the other ofsaid sound passages, and means supporting said separator in said shellin spaced relation thereto.

13. A loudspeaker driver unitas defined in claim l2, wherein the meansfor supporting the separator means includes an annular gasket havingsound openings therethrough disposed between said shell and a portion ofthe diaphragm.

14. A loudspeaker driver unit as defined in claim 12, wherein the meansfor supporting the separator means includes an apertured centeringspider carried by said shell in the neck thereof and engaged about theneck of said separator means.

l5. A loudspeaker driver unit comprising a shell, a magnetic potassembly mounted in said shell in spaced relation thereto and definingwith said shell a sound passage therebetween, a central pole-piece insaid pot assembly, said pole-piece having at least one openingtherethrough, a vibratable diaphragm mounted in said shell at one end ofsaid pole-piece and overlying the latter in spaced relation to saidpole-piece and to said shell, a barrier at the other end of saidpole-piece and having a central opening therethrough defining an outletthroat in communication through the opening in said pole-piece with thespace between said diaphragm and said pole-piece, said barrier beingspaced from said shell and defining therewith an annular outlet throatconcentric with the central outlet throat through the barrier, and thelast-mentioned outlet throat being in communication through the spacebetween said magnetic pot assembly and said shell with the space betweensaid diaphragm and said shell.

16. A loudspeaker driver unit comprising an axially extended generallycylindrical outer shell, a vibratable diaphragm mounted in said shell atone end thereof, means in said shell for vibrating said diaphragm, saidshell having a reduced hollow neck adapted to be connected to aloudspeaker horn, means defining a pair of acoustically isolated soundpassages leading from opposite sides of said diaphragm to said hollowneck, said i last-mentioned means including a barrier mounted in saidshell at the other end of the same and on the side of the diaphragmvibrating means opposite said diaphragm, said barrier having a centralopening therethrough constituting a central outlet throat for one ofsaid sound passages, said barrier being spaced from said reduced neckand defining with said neck an outlet throat for the other of said soundpassages concentric with the first-mentioned outlet throat, the centraloutlet throat through the barrier and its sound passage beingsubstantially straight and short, and the outlet throat between thebarrier and the shell and its sound passage being relatively long andtortuous.

17. A loudspeaker driver unit comprising a shell, a diaphragm in saidshell, means in said shell for vibrating said diaphragm, means formounting the diaphragm vibrating means in spaced relation to said shellto form a sound passage between said shell and the diaphragm vibratingmeans leading from one side of said diaphragm, said diaphragm vibratingmeans having means providing a sound passage therethrough leading fromthe other side of said diaphragm, a neck on said shell forming an out-1ct throat for the first-mentioned sound passage, and barrier meansdisposed in said shell and defining an outlet throat for thesecond-mentioned sound passage, said sound passages being acousticallyisolated one from the other, and said outlet throats also beingacoustically isolated one from the other and extending coaxially in thesame direction.

18. A loudspeaker driver unit as dened in claim 17, wherein saiddiaphragm and said barrier means are disposed on the respective oppositesides of said diaphragm vibrating means.

19. A loudspeaker driver unit as defined in claim 17, wherein thediaphragm vibrating means comprises a magnetic pot assembly including acentral pole-piece having at least one opening therethrough, and havinga plate at one end of said pole-piece provided with a central openingtherethrough, said barrier means being Supported on said plate, and thethroat of said barrier means being in communication with the openingthrough said pole-piece through the opening in said plate.

References Cited in the file of this patent UNITED STATES PATENTS1,930,915 Wente Oct. 17, 1933 2,084,944 Cornwell June 22, 1937 2,367,026Hutter Jan. 9, 1945 2,429,470 Knowles Oct. 2l, 1947 2,440,439 GilmanApr. 27, 1948 2,534,040 Lindley Dec. 12, 1950 2,549,963 De Buer et al.Apr. 24, 1951 2,642,947 Heidrich June 23, 1953 OTHER REFERENCES Olson etal.: Publication, A Compound Horn Loudspeaker, Journal of the AcousticalSociety of America, vol. 8, pp. 48-52, July 1936.

